PostgreSQL is strict about the usage of `DISTINCT` and `ORDER BY`, which
one of the tests demonstrated. The order clause is never going to be
relevant in the query we're performing, so let's just remove it
entirely.

THe only reason we were allocating an array is to get the "missing_keys" variable in scope of the error message generator. Guess what? Arrays kinda take up a lot of memory, so by replacing that with a nil, we save:
35,303 bytes and 886 objects per request

In the `tag_options` method an array is used to build up elements, then `Array#*` (which is an alias for `Array#join` is called to turn the array into a string. Instead of allocating an array to build a string, we can build the string we want from the beginning.
Saved: 121,743 bytes 893 objects

We can save a few objects by freezing the `replacement` string. We save a few more by down-casing the string in memory instead of allocating a new one. We save far more objects by checking for the default separator `"-"`, and using pre-generated regular expressions.
We will save 209,231 bytes and 1,322 objects.

If we don't mutate the `recall` hash, then there's no reason to duplicate it. While this change doesn't get rid of that many objects, each hash object it gets rid of was massive.
Saves 888 string objects per request, 206,013 bytes (thats 0.2 mb which is kinda a lot).

Instead of calling `sub` on every link_to call for controller, we can detect when the string __needs__ to be allocated and only then create a new string (without the leading slash), otherwise, use the string that is given to us.
Saves 888 string objects per request, 35,524 bytes.

When `defaults[key]` in `generate` in the journey formatter is called, it often returns a `nil` when we call `to_s` on a nil, it allocates an empty string. We can skip this check when the default value is nil.
This change buys us 35,431 bytes of memory and 887 fewer objects per request.
Thanks to @matthewd for help with the readability

content_tag's first argument is will generate a string with an html tag so `:a` will generate: `<a></a>`. When this happens, the symbol is implicitly `to_s`-d so a new string is allocated. We can get around that by using a frozen string instead which
This change buys us 74,236 bytes of memory and 1,855 fewer objects per request.

The instrument method creates new strings, the most common action to instrument is "!render_template` so we can detect when that action is occurring and use a frozen string instead.
This change buys us 113,714 bytes of memory and 1,790 fewer objects per request.